This study will characterize and pharmacologically the membrane currents of vertebrate neuron somata. Particular attention will be paid to transmitter and synaptic regulation of such currents. The preparations to be used are bullfrog paravertebral ganglion (fresh or cultured), rat superior cervical ganglion, guinea pig hippocampal slices, olfactory cortex slices and cultured hippocampal neurons. These neurons will be voltage clamped using one or two microelectrodes. Calcium currents and 4 distinct potassiom currents will be studied. These potassium currents are IDR (conventional delayed rectifier), IC (calcium-activated), IA (transient) and IM (a novel slow K-current operating in the subthreshold range). The possibility that adrenergic stimulation reduces ICA in mammalian neurones, and that nuscarinic cholinergic stimulation reduces IM, in sympathetic and central neurones, will be examines. Finally, the operation of these currents in conjunction will be modelled on a computer, to determine their significance in controlling nervous excitability in normal and pathological conditions.